Drying plants for wooden sheet material



Nov. 8, 1%55 A. s. MORCH DRYING PLANTS FOR WOODEN SHEET MATERIAL Filed May 4, 1953 INVENTOR.

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DRYING PLANTS FOR WOODEN SHEET MATERIAL Arne Siiren Miirch, Sundsvall, Sweden Application May 4, 1953, Serial No. 352,685

2 Claims. (Cl. 3486) The present invention relates to drying plants for wooden sheet material such as veneer, plywood, wallboard and the like, of the type comprising superimposed conveying tracks for the material being dried in a drying passage in the housing of the plant, means being provided to convey the sheet material in the longitudinal direction of said drying passage, a longitudinal air duct being also provided to supply heated air to the drying passage.

An object of the invention is to design a drying plant of said type so as to operate at a minimum of heat losses.

A further object of the invention is to provide means whereby the material being dried receives air of a temperature and to a quantity corresponding, as far as possible, to the need in the part of the drying plant, in which the material is passing.

A still further object of the invention is to provide inlet openings for heated air to the drying passage at suitable points along the length and height of the drying passage to enable a suitable distribution of the air to various points of said passage, whereby an even drying operation may take place.

The invention aims further at providing means to pre treat the material before entering the drying passage proper whereby a suitable preheating thereof may be performed.

Still another object of the invention is to adapt the air pressure in various points of the plant so as to obtain a suitable circulation of the drying air without material losses of heated air to the outer atmosphere.

An embodiment of the invention will be more clearly described hereinafter by way of example, reference being had to the accompanying drawing, in which Fig. 1 dia grammatically shows a vertical sectional view longitudinally of the drying plant housing, Fig. 2 is a similar sectional view of the ends of the drying plant on an enlarged scale, and Fig. 3 a corresponding transverse section through the drying plant at a pair of lateral inlet means or manifolds.

In the drawing, the drying passage proper is designated by 1 and the ante-chamber with 2. The ante-chamber communicates with the drying passage 1 at a section 3, contingently provided with suitable tightening means, in which section the intake end of the drying passage proper is located. The sheet material to be dried is introduced into the ante-chamber 2 through the generally open end 4. The dried material is discharged at the generally open exit end 5 of the drying passage. Conveying tracks for the material extend through the antechamber and the drying passage, said tracks being arranged in three stories above each other in the embodiment shown and consisting of roller tracks 6, 7, 8 driven by chain-transmission means.

Extending above the drying passage 1 is a longitudinal air duct 9, from which pairs of lateral inlet passages or manifolds 10, 11 are branched off at various points along the length thereof. Provided at every lateral inlet point is a vertical lateral passage on each side of the drying passage. The outer wall of the lateral passage States Patent 0 2,722,752 Patented Nov. 8, 1955 is inclined from above in a downward direction inwardly toward the bottom of the drying passage. As shown in Fig. 3, the vertical lateral walls of the drying passage are provided at the lateral inlets with openings 14, 14 on a level with the corresponding conveying tracks 6, 7, 8. For each opening the inflow of air may be controlled by means of a damper 15. If desired, one damper 16 is sufficient in every transition between the longitudinally extending duct 9 and the lateral inlet passages 10, 11. Instead, the transition openings between the passage 9 and the lateral passages may have a size adapted to the requisite quantity of air. For the propelling of the air in the passage 9 there is provided a diagrammatically indicated fan 15.

Before the air from the passage 9 flows down in the lateral passages 10, 11, it passes a radiator 12. Such radiators may be arranged in front of every lateral passage, and said radiators may be of a size such that the air, on having passed through the same, obtains a temperature adapted to the corresponding part of the drying passage.

The air, on its having flown into the drying passage 1 through the lateral inlets, will then flow back in the longitudinal direction of the passage against the direction of movement of the material fed forward here, the material being thus dried. The moist air, the wet air, escapes from the drying passage through an outlet opening 17 in the upper wall of said passage. A portion of the wet air is sucked back into the passage 9 by means of the fan 15', while the remainder is conveyed through a connecting passage 18 and through a heat exchanger 19 to the outlet end of the ante-chamber 2. For the purpose in consideration there is provided according to the drawing, a diagrammatically illustrated ventilator 20 in the passage 18. The quantity of air in the connecting passage may be controlled by means of dampers 21, 22 in the inlet of the connecting passage and/or in the outlet thereof. For the introduction of the wet air into the ante-chamber lateral passages or manifolds may be arranged similarly to the lateral passages 10 and 11 in the drying passage 1 proper. The wet air thus carried away is replaced by dry fresh air passing through the heat exchanger 19 and introduced through a conduit 23 into the inlet end of the passage 9 in front of the fan 15. An inlet socket for the fresh air to the heat exchanger is denoted by 24.

In the heat exchanger 19 the temperature of the wet air is reduced simultaneously with the heating of the fresh air. The wet air entering the ante-chamber preheats the wooden material in a suitable manner. The free water in the cells is heated by the heat contents of the wet air, while condensation on the material sets in at the same time. Hereby the conveyance of water from the interior of the material to the surfaces thereof is facilitated during the drying process in the drying passage.

In case the material is fed in continuously into the ante-chamber at the intake end 4 the latter must be open. In order that a flow of dry fresh air into the ante-chamber shall be avoided as far as possible, an outlet or stack 25 is provided at the intake end, said outlet being provided with a suction ventilator 26, which is balanced relatively to the ventilator 20 in the connecting passage 18, in a manner such that the air pressure in the intake opening 4 will equal the pressure of the external air as far as possible.

The number of lateral passages 10, 11, through which dry air is introduced into the drying passage, may vary, which is also the case with the location of these passages according to the material to be dried. In the example shown, three lateral inlet points are provided in the feeding direction of the material, counted before the section marked by the line FF, in which section the fiber saturation point of the material during the drying process in the passage is conceived of as being attained, and after said section there are also provided two further inlet ports. 7 i

The invention is not restricted to the construction shown and described, which is only intended to represent an example.

What I claim is:

1. A drying plant for wooden sheet material such as plywood, wall board and the like, comprising a housing defining a drying passage with an intake and an outlet for the material to be dried and an air duct extending in the longitudinal direction of the drying passage and provided with an inlet for air at the end corresponding to the intake end of said drying passage and with lateral outlets at various points of its length, means forming conveying tracks in interspaced superimposed relation in the drying passage for conveying the material in the longitudinal direction thereof, air heating means in said air duct, lateral manifolds communicating with said lateral air outlets to receive heated air therefrom, said manifolds having outlets at various heights to supply the heated air to the spaces between the superimposed tracks in the drying passage, means to circulate air through the air duct to the manifolds and into the drying passage and in the longitudinal direction thereof back to the intake end for the material to be dried and back to the air duct, an ante-chamber for preheating of the material at the intake of the drying passage, a duct connecting the intake end of said drying passage with said ante-chamber for conveying to said ante-chamber part of the hot wet air returned to the intake end of said drying passage thereby to preheat the material in said ante-chamber, and a heat exchanger in said wet air duct for withdrawing heat from the wet air, the heat absorbing side of said heat exchanger having passages for fresh air connected with the air inlet to said longitudinally extending air duct.

2. A drying plant as claimed in claim 1 and further comprising a wet air stack at the intake end of said ante chamber, a ventilator in said stack and a further ventilator in the connection duct for wet air, said ventilators being adapted in relation to each other to maintain a desired air pressure in the ante-chamber.

References Cited in the file of this patent UNITED STATES PATENTS 947,306 Morey Jan. 25, 1910 1,656,802 Vance Jan. 17, 1928 1,995,999 Oman Mar. 26, 1935 FOREIGN PATENTS 130,363 Sweden Dec. 19, 1950 

